JP2002536634A - Particle mass difference monitor that internally corrects volatile loss - Google Patents

Abstract

(57) [Summary] The mass of the particulate matter in the gas stream (42) containing particles is measured using a first mass detector (50A) and a second mass detector (50B). By the switching means (48A, 48B, 56), an air flow containing particles and an air flow substantially the same as that containing particles but not containing particles are continuously connected to the first mass detector and the second mass detector, respectively. Mating during the measurement period. The difference between the measurement provided by the first mass detector (50A) and the measurement provided by the second mass detector (50B) for each successive measurement period is determined. This difference internally corrects for volatile losses that occur during the measurement period. From this difference, the mass or concentration of the particulate matter in the gas stream containing the particles is determined. An embodiment of a single detector (10 ', 40') is also shown.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates generally to the measurement of particulate matter suspended in a fluid medium, and in particular, to particulate matter suspended in ambient air or other gaseous environments, such as diesel exhaust, mines, chimneys, industrial equipment, and the like. The measurement of at least one of the mass and the concentration of the particulate matter.

[0002] Particles are a general term for concentrated solids, semi-solids, or liquids that result from natural or man-made processes and that can be suspended in air or other fluid media due to their small size.

[0003] The measurement of particulate matter in ambient air is important for a variety of reasons, the most important of which is the effect on health. It is known that inhaling suspended particulate matter has various adverse effects on health. As a result, environmental regulators around the world are calling for monitoring of particulate matter. The level is measured in concentration conditions, ie in micrograms of particulate matter per cubic meter of air. The standard techniques for this measurement are defined as mass measurement utilizing a filter to trap particulate matter and the total volume of air filtered through a filter over a period of time. Although there are various techniques available to accurately measure the flow rate through the filter over time (and therefore the volume of the sampled air), the nature of particulate matter in the environment is complex and the amount of deposition on the filter is low. Inconsistent and surprisingly, mass measurement is not easy.

[0004] This problem associated with the measurement of particulate matter in ambient air is well known. The mass of the particles used as the basis for the mass concentration calculation is defined by the mass captured on the filter, but this is not necessarily the mass when the particles are present in ambient air, thus causing such uncertainties . Unlike the main criteria for measuring air pollutants, substances defined as particulate matter can change their mass as a result of gaining or losing volatiles that bind the particulate matter to the filter. Atmospheric pollutants exist as distinct molecular species (SO ₂ , O ₃ , CO, etc.), but particulate matter is a combination of substances with different volatilization rates, reactivity, desorption, absorption, and adsorption Can be Furthermore, the mass of particulate matter deposited on the filter depends on the filter material itself, the particulate matter already collected on the filter, the surface velocity passing through the filter, and the pressure loss at the filter, as well as humidity, temperature and It is also affected by the composition of the airflow passing through the trapping material.

[0005] In an effort to quantify the mass of particulate matter, direct and indirect methods have been used. However, any of the methods currently used have limitations in measuring the actual mass of particulate matter present in suspended form. Direct mass measurements, typified by the gravimetric determination of substances trapped on a carrier such as a filter, are susceptible to instrumentation, for example, due to temperature and pressure changes and the loss of volatile components that are not easily quantified.
On the other hand, indirect methods such as light scattering are inherently inaccurate because there is no physical correlation between particle properties and particle mass.

[0006] Particle mass difference microbalances using a pair of vibrating quartz detectors have been previously proposed to compensate for instrument effects in direct mass measurement. In this early approach, a particle-containing airflow impinges on a first detector and a particle-free airflow impinges on a second detector. The second mass detector is used as a reference to eliminate the influence of the detector instrument from the mass measurements provided by the first detector. U.S. Pat. No. 5,571,945 discloses a similar measurement approach using a pressure sensor to measure the differential pressure between a pair of particulate traps. US Patent 5,3
No. 49,844 discloses a similar approach using a filter that vibrates in a direction substantially perpendicular to the filter plane. However, volatile losses have not been evaluated in these early systems.

[0007] As a result of the above difficulties, the current reference method in the United States relies on technology that does not always allow accurate measurement of particle mass as it exists in the air undisturbed. The reference methods include equilibrating the filter over a range of temperature and humidity conditions, weighing the filter before collection, installing the filter on a manual sampler, sampling ambient air (24 hours), and removing the filter from the sampling device. Removal, post-collection conditioning at the same equilibrium conditions as before, and final post-collection weighing. The intent of this methodology is to provide a stable set of measurements between the same samples.

[0008] However, for the above reasons, the results based on this method, even if roughly, do not allow for measurements with specified accuracy. That is, how accurately does the mass measured from the filter represent the mass of the particles when present in the atmosphere. This is a serious problem and it must be acknowledged that these measurements are only indicative of the particle level. As a result, the current standard law is:
It merely represents a standardized approach, not a scientifically sound measurement of particulate matter in air.

[0009] Volatile components have a confusing effect on these measurements. Although the filter is attached to the sampling device, the variability of important factors such as temperature and humidity that affect the reaction performed on the filter is not clear. During sampling, the mass of the filter and the filter increases dramatically during periods of low temperature and high humidity (nighttime), and when the temperature increases and humidity decreases (daytime), the semivolatiles can decrease significantly. is there. These same effects could be associated with changes in air mass or other weather events. In addition, the collection filter may be subjected to widely varying high or low temperatures before sampling is complete and before removal from the sampler or during transport to the laboratory for conditioning and weighing.

[0010] Not only does the mass of the trapped particulate matter and the filter fluctuate depending on the conditions to which they are exposed, but also the flow of air through the filter creates a pressure differential across the filter, which increases the volatility of the particulate matter. In some cases, the ingredients are removed. In short, the interaction between the particles and the filter tends to change the nature of the particulate matter as soon as it is trapped, so that a certain amount of particulate matter can be compared to when the particulate matter is suspended in ambient air. Affects measurement accuracy. As health concerns have increased and the sensitivity of measurement devices has increased, there has been a trend to measure finer particulate matter, for example, particles smaller than 2.5 microns. The smaller the particles, the more important the effect of volatile losses on the mass measurement. Therefore, there is a strong demand for a measuring device capable of accurately measuring the mass or concentration of particulate matter in environmental air or other atmospheric environment.

[0011] The present invention provides a method and apparatus that overcomes the above-mentioned problems, and provides a capture that enables accurate quantitative analysis of particulate matter, including its volatile components, in ambient air or gas. It offers for the first time direct mass measurement based on collections. The measurement method of the present invention not only eliminates the influence of the detector instrument, but also compensates for volatile losses internally. For the purposes of this disclosure, "volatile loss" is used in a broad sense to include evaporation, absorption, adsorption, desorption, reactivity, and other effects that affect the mass of collected particulate matter.

The present invention has a dual detector version and a single detector version.

[0013]Double detector  According to the principles of the present invention, for measuring the mass of particulate matter in an airflow containing particles
Apparatus comprises a first mass detector, a second mass detector, and no particles.
A first means for providing a particle-free airflow substantially identical to the airflow containing the particles;
Steps are included. By the switching means, during the continuous measurement period, the air flow containing the particles
And the air flow containing no particles alternately with the first mass detector and the second mass detector.
It is selectively passed to the outlet. A first mass for each of said successive measurement periods
Between the measurement obtained by the detector and the measurement obtained by the second mass detector
The difference is calculated. This difference internally compensates for the volatile losses that occur during the measurement period. particle
The mass or concentration of the particulate matter in the air stream containing is determined from this difference.

[0014] Advantageously, the first means for providing a particle-free airflow comprises particle removal means for removing substantially all particulate matter from the particle-containing airflow. It is optimal that the particle removing means removes particulate matter from the gas stream containing the particles without substantially affecting the temperature, pressure and flow rate of the gas stream. Such particle removal is preferably performed using an electric dust collector. The electric precipitator is preferably operated with positive corona and low current.

[0015] The first and second detectors each include a vibrating element microbalance. Each detector comprises a hollow element that oscillates in a clamp-free mode, with a filter supported at the free end of the element. The first mass detector plays a role of trapping particulate matter from the gas stream when the gas stream containing the particles flows through the detector. Advantageously, the fluid control means is able to maintain substantially the same airflow rate at each detector filter during each measurement period. In the form of a vibrating element microbalance, the measurement of the mass obtained by the mass detector is advantageously based on the change in the vibration frequency of the vibrating element over time.

According to another aspect of the present invention, the switching means of the mass measuring device causes (a) an airflow containing particles to flow through the first mass detector during each even-numbered period of the continuous measurement period,
At the same time, an air stream containing no particles flows through the second mass detector, and (b) during each odd-numbered period of the continuous measurement period, the air stream containing the particles flows through the second mass detector. At the same time, an air flow containing no particles is passed through the first mass detector. Detectors passing through an air stream containing particles measure the gained mass, whereas detectors passing through an air stream containing no particles measure the mass lost due to the volatile components of the particulate matter. To determine the particulate matter, the measured loss mass is added to the measured gain mass.
The duration of each successive measurement time is short, preferably 15 minutes, and currently less than 1 minute is considered most preferred.

In another aspect of the invention, the measurements obtained by the first and second mass detectors are each a mass ratio, which can limit the accumulation of calibration errors in the mass measurement.

In another aspect of the invention, a corrected mass concentration is calculated from a corrected mass ratio combining the mass ratios from the first and second mass detectors.

Also, the present invention is a significant improvement over current particle mass difference measurement systems. In such a system, an air stream containing particles is passed through a first mass detector,
A particle-free airflow is passed through the second mass detector. The second mass detector is used as a reference to eliminate the effects of the detector instrument from the measurements obtained with the first mass detector. According to the present invention, such a particle mass difference measuring system alternately switches an airflow containing particles and an airflow not containing particles to a first mass detector and a second mass detector during a continuous measurement period. This is provided by including switching means for flowing. In this way, a correction is internally made for the volatile losses occurring during successive measurement periods.

In yet another aspect of the present invention, there is provided an apparatus for measuring the mass of a particulate matter containing a volatile component in an air stream containing the particles. The apparatus includes means for dividing an air flow containing particles into a first air flow and a second air flow, and guiding the first air flow to continuously flow through the first mass detector to guide the second air flow. And means for removing substantially all of the particulate matter from each of the first and second air streams when the means for continuously flowing through the second mass detector and the corresponding means for removing particles are actuated. First and second airflow particle removing means are included. During successive measurement periods, the control means alternately activates only one of the first airflow particle removal means and the second particle removal means. During each successive measurement period,
A difference between a first measured value obtained by the first mass detector and a second measured value obtained by the second mass detector is measured. This difference compensates internally for volatile losses that occur during the measurement period. From this difference, the mass or concentration of the particulate matter in the gas stream containing the particles is determined.

According to yet another aspect of the present invention, a method for measuring particle mass difference is improved. In a known method, an air stream containing particles is passed through a first mass detector. The first mass detector collects the current particle sample from the airflow during the current measurement period and measures the resulting mass. The second mass detector is used as a reference and eliminates the effects of the detector instrument. The present invention improves on this method by the second mass detector also measuring changes in the properties of the particles that occur during the current measurement period. This change in the properties of the particles typically includes the mass lost due to volatilization of the collected volatile particles. The mass loss due to volatilization measured by the second mass detector is added to the acquired mass measured by the first mass detector, and a corrected particle mass measurement is performed for the current measurement period. The measured loss mass occurs in the initially collected particle sample during the current measurement period, but this initially collected particle sample is not detected by the second mass detector during an earlier measurement period. It was collected in. The current measurement period and the previous measurement period must be sufficiently short so that the amount of volatilization during the current measurement period between the initially collected sample and the current particle sample is substantially the same. Is preferred.

The present invention provides various significant benefits and advantages. The biggest of these is
It is an intrinsic correction for the volatilization losses that occur during the measurement period. Using a short measurement time ensures that the mass measurement includes an accurate indication of the volatile mass associated with the collected particles under any chosen temperature, including various environmental temperature conditions. Since both mass detectors are constantly observing the same collector (eg, filter) and instrument artifacts, subtracting the measurement of one detector from the measurement of the other detector will result in a lower The compensation will be effective and complete. The use of an electrostatic precipitator for particle removal is preferable in preventing pressure disturbance, and due to the different volatility,
One mass detector does not interfere with the other mass detector. In addition, the electrostatic precipitator facilitates instantaneous switching of the particle components of the airflow with electrical on-off without the need for mechanical action. Switching the airflow also effectively doubles the collector life as compared to a single collector system. Furthermore, if the operation is different 2
If one measuring device is driven in line with one at ambient temperature and another at fairly high temperature in accordance with the principles of the present invention, the volatile and non-volatile nature of particulate matter in the environment The distinction becomes possible.

[0023]Single detector  According to the principles of the present invention, an apparatus for measuring the mass of particulate matter in an air stream containing particles
Has a mass detector, and an air stream containing the particles except for the particles.
A first means for providing a particle-free airflow that is identical is included. Switching means
Thus, during a continuous measurement period, an airflow containing the particles and an airflow not containing the particles
Are alternately passed through the mass detector. Obtained with the mass detector during the current measurement period
The difference between the measured value and the measured value obtained by the mass detector during successive measurement periods is calculated.
It is. This difference internally compensates for the volatile losses that occur during the current measurement period. This difference
The mass or concentration of the particulate matter in the gas stream containing the particles is determined. Contains particles
A first means for providing an airflow that is substantially free from the airflow containing said particles
It is advantageous to have a particle removing means for removing the particulate matter. The grain
Particle removal means removes particles from an air stream containing particles without affecting air temperature, pressure, and flow rate.
It is optimal to remove dendrites. Such particles are removed using an electrostatic precipitator.
It is preferable to carry out. Electrostatic precipitators are preferably operated with positive corona and low current.
Made.

[0024] The mass detector may be a vibrating element microbalance. The detector has a hollow element that oscillates in a clamp-free mode, with a filter supported at the free end of the element. When passing an airflow through the detector, the filter serves to trap particulate matter from the airflow containing the particles. Advantageously, during each measurement period, the fluid control means maintains a substantially constant air flow at the filter of the detector. In the form of a vibrating element microbalance, the measurement of the mass obtained with the mass detector is advantageously based on a change in the vibration frequency of the vibrating element detected over time.

According to another aspect of the present invention, the switching means of the mass measuring device causes (a) an air flow containing particles to flow through the mass detector during an even numbered period of the continuous measurement period, and (b) continuous measurement. During the odd numbered periods of the period, the particle-free airflow is passed to the mass detector. When the detector is passed through an air stream containing particles, the detector measures the acquired mass. When a particle-free gas stream is passed through the detector, the detector measures the mass lost due to volatilization of volatile components of the particulate matter. The measured loss mass is added to the measured gain mass to determine the mass of the particulate matter. Each successive measurement period lasts for a short time, but is preferably 15 minutes or less, and currently considered to be most preferred is about 1 minute or less.

In another aspect of the invention, each measurement obtained with the mass detector is a mass ratio, which limits the accumulation of calibration errors in the mass measurement.

In another aspect of the invention, the corrected mass concentration is derived from the corrected mass ratio by combining the mass ratio measurements obtained from the mass detector during two consecutive measurement periods. Is calculated.

The present invention also provides significant improvements over conventional particle mass difference measurement systems. In such a system, an airflow containing particles flows through the first mass detector, and an airflow containing no particles flows through the second mass detector. A second mass detector is used as a reference to eliminate the effects of the detector instrument from the measurements obtained at the first mass detector. According to the present invention, the particle mass difference measurement system includes switching means for alternately flowing an airflow containing particles and an airflow not containing particles to one mass detector during a continuous measurement period. It is improved by. In this way, corrections for instrument artifacts and volatile losses that occur during successive measurement periods are made internally, eliminating the need to calibrate and match multiple detectors, reducing complexity and cost of the measurement device. I do.

In another aspect of the present invention, there is provided an apparatus for measuring the mass of a particulate matter in an air stream containing particles, including its volatile components. The apparatus includes a mass detector, a means for directing the airflow to flow continuously through the mass detector, and a particle removal means for, when activated, removing substantially all particulate matter from the airflow. . The control means alternately activates the particle removal means during successive measurement periods. The difference between the first measurement obtained with the mass detector and the second measurement obtained with the mass detector during successive measurement periods is measured. This difference internally corrects for volatile losses that occur during the measurement period. From this difference, the mass or concentration of the particulate matter in the airflow is determined.

According to yet another aspect of the present invention, a method for measuring particle mass difference is improved. In a known method, an air stream containing particles is passed through a first detector. The first mass detector collects the particle sample from the airflow during the current measurement period and measures its acquired mass. The second mass detector is used as a reference to eliminate the effects of the detector instrument. The present invention not only eliminates the effects of the detector instrument, but also uses this method by using a single mass detector to effectively measure the change in particle properties that occurs during the current measurement period. Improve. This change in particle properties usually also includes the mass lost due to volatilization of the collected volatile particles. The mass lost due to volatilization measured at the mass detector is added to the acquired mass measured at the mass detector to obtain a corrected particle mass measurement during the current measurement period. The measured loss mass occurs during successive measurement periods in the initially collected particle sample (ie, during the period immediately before or immediately after the current measurement period), and the initially collected particle sample It was collected by the mass detector during the previous measurement period. The current measurement period and the subsequent measurement period may be sufficiently short so that the volatilization during the subsequent measurement period of the initially collected sample and the current particle sample is substantially the same. preferable.

The present invention provides various significant benefits and advantages. The largest of these is the intrinsic correction of the volatile losses that occur during the measurement period. Using a short measurement time ensures that the particle mass measurement includes an accurate indication of the volatile mass associated with the particles collected under any selected temperature, including changes in ambient temperature. The mass detector is
During a set of consecutive measurement periods, substantially the same collector (e.g., filter) and equipment artifacts are observed, so that the measurements during one measurement period are separated from the measurements during another measurement period. When deducted, compensation for the effects of the instrument is effective and complete. The use of an electrostatic precipitator for particle removal is preferred to prevent pressure disturbances. The electric precipitator does not require a mechanical operation, and facilitates instantaneous switching of the particle components in the airflow by electric on-off. Furthermore, switching airflow effectively doubles the life of the collector as compared to a continuous particle collector system. Furthermore, when two measuring devices operating differently according to the principle of the present invention are driven side by side at one at ambient temperature and another at considerably high temperature, it is possible to distinguish between volatile and nonvolatile particulate matter in the environment. It can be performed. The use of a single detector has additional cost and reliability advantages.

Various aspects, features, and advantages of the present invention will be more readily understood from the detailed description of the preferred embodiments, when read in connection with the accompanying drawings.

The goal of the present invention is to accurately measure the mass of particulate matter suspended in ambient air (or other gaseous environment), including its volatile components. In a dual detector embodiment, the first mass detector and the second mass detector alternate between a particle-containing airflow and a substantially identical but particle-free airflow during successive measurement periods. It is performed by flowing through a vessel. Take the difference between the measurements obtained with the first and second mass detectors in a sufficiently short measurement time and add the mass lost due to volatilization during the measurement period to the measured gain mass of the collected particulate matter. Thus, an accurate measurement of the total particle mass is performed.

One embodiment of the dual detector of the particle mass measurement device of the present invention is illustrated in FIG. The device 10 has two identical sides "A" and "B" (therefore, the numbers associated with each side are also labeled accordingly). Each side of device 10 "
A "and" B "include inlets 12 in air communication with selectively operable particle remover 14 and mass detector 16. Each side" A "of apparatus 10.
At "" and "B", an air stream 18 containing particles enters each inlet 12, passes through each selectively operable particle remover 14, and continuously flows through each mass detector 16. The term "" is used herein to broadly imply the interaction of airflow with a mass detector. Such interactions can take different forms depending on the nature of the mass detector used.

The inlet 12 typically includes a separator for pre-separating particles larger than a predetermined “cut-off” size from the gas stream containing the particles. For example,
Inlets having at least one of a PM10 and PM2.5 separator are known and commercially available.

The air stream containing particles entering the inlet 12 then passes through a selectively operable particle remover 14. When activated, the particle remover 14 provides the temperature of the airflow,
Substantially all particulate matter is removed from the air stream with little effect on pressure and flow rate. It is advantageous to remove such particles using the same general-purpose type electrostatic precipitator that is commonly used in air cleaning devices. To reduce ozone production, a positive corona and an electrostatic precipitator operating at very low current, for example on the order of tens of nanoamps, are preferred. The current must be sufficient to cause the precipitator to remove substantially all particulate matter.

The particle removers 14A, 14B operate selectively and alternately during successive measurement periods, requiring the removal of particulate matter from one airflow 18A and then the other airflow 18B during successive measurement periods. is there. For example, during the first measurement period, the particle remover 14A is turned on, and the particle remover 14B is turned off. Particle remover 14B during the next measurement period
Is turned on, and the particle remover 14A is turned off. This alternating actuation pattern continues during successive measurement periods. Advantageously, each period lasts for a relatively short time, preferably on the order of 15 minutes or less, more preferably on the order of 5 minutes or less, and most preferably on the order of 1 minute or less. The air flows 18A, 18B emerging from the particle removers 14A, 14B are constantly flowing to the respective mass detectors 16A and 16B during successive measurement periods.

As the mass detector 16, other direct or indirect mass detectors such as a quartz crystal microbalance, a β-ray absorption monitor, and a pressure loss monitor can be used, but a tapered hollow element vibrating microbalance is considered to be preferable. . The latter device is preferable because it has high sensitivity to mass, can perform real-time measurement, is mass measurement based on direct inertia, and has high collection efficiency by utilizing filtration.

High sensitivity to mass is important because the masses that need to be measured are in the microgram and sub-microgram range. Real-time measurement is important because mass volatilization occurs in a short time frame. Direct mass measurement is desirable because it avoids ambiguity in measured values and also allows for traceable calibration with mass standards. Filtration guarantees high collection efficiency. A suitable tapered element vibrating microbalance is described in US Pat. No. 4,391,338, with further background information in US Pat. No. 3,926,271. The teachings of these two patents, all of which are incorporated herein by reference.

In a preferred microbalance, the tapered hollow element oscillates in a clamp-free mode. A filter is attached to the free end of the device and serves to trap particulate matter from the gas stream containing the particles. This airflow passes through the filter and then through the hollow element, the vibration frequency of the hollow element changing with the mass load of the filter, which can be converted into a mass measurement. For the purposes of the present invention, the change in the vibration frequency of the vibrating element in connection with each measurement period is converted into a mass ratio (ie the mass change with respect to the measurement time interval), and the mass concentration corrected as described in detail below. Is obtained.

A tapered hollow element vibrating microbalance is preferred, but of other types or shapes, such as operating in other modes such as non-tapered, tuning fork or U-shaped, or clamp-free mode, or A collector, a collision plate, or other particle collector that oscillates in a direction substantially perpendicular to the plane of the collector may also be used as the mass detector.

In operation, particle remover 14B is on when particle remover 14A is off, or
It is off when the removed particle remover 14A is on. When the particle remover 14A is off
In this case, the mass change at time Δt and the frequency change due to the
Dispenser 16A measures the effective mass. M_Aeff= M_P+ M_Pv+ ΑM_G+ ΒΔT + γΔP (1) where M_P= Non-volatile component of particle mass M_Pv= Volatile component of particle mass αM_G= Acquisition / desorption of filter and gas acquisition by evaporation of deposited material
Or loss mass βΔT = effective mass equivalent of frequency change due to temperature change ΔT during time Δt γΔP = effective mass equivalent of frequency change due to pressure change ΔP during time Δt (β
ΔT and γΔP indicate major instrument artifacts) During the same time Δt, on side “B”, its particle remover 14B is on,
M_PAnd M_PvIs removed and not detected by the mass detector 16B. Also, M_Beff= ΒΔT + γΔP (2) Therefore, M_Aeff-M_beff  = M_P+ M_Pv+ ΑM_G+ ΒΔt + γΔP- (αM_G+ ΒΔT + γΔP) = M_P+ M_Pv (3) During the next measurement period or measurement interval, the particle remover 14A is on and the particle remover 14B
Is off. For example, the adsorption / desorption effect of gas or vapor
To maintain the same particulate matter history on both detectors so that accurate subtraction is possible,
These time intervals are relatively short.

The mass detector 16 corresponding to the particle remover 14 that does not operate during the particle measurement time,
It provides a mass measurement indicating the mass of the particulate matter collected during that period, ie, the acquired mass. Measured mass loss due to volatilization during that period does not include particles (
Airflow is provided by another mass detector (through the operation of the particle remover). Subtracting the two mass measurements and substantially adding the lost mass to the measured gained mass provides an accurate measurement of the mass of the corrected particulate matter.

In practice, measurements can be made based on mass ratio by utilizing the switching time on a suitable time basis. Unlike a total mass measurement, by subtracting the mass ratio, a small calibration error in the measurement system will result in a comparable final error. If the masses were used strictly, this error would accumulate to unacceptable levels over the duration of the monitoring period, and the total masses at both detectors would vary from one another.

FIG. 2 shows an example of how the mass changes over four consecutive measurement periods, measured with the detectors 16 A, 16 B of the device according to the invention. The corrected mass concentration can be calculated according to the following relation: ^{(-1) n + 1 (Δm} B / Δt) n + (- 1) n (Δm A / Δt) n = (Δm / Δt) _n (4) and (MC) _n = (Δm / Δt) _n (1 / F) = Δm / ΔV _n (5) where Δt represents a time interval during the measurement period, and n Represents the measurement time index, where the airflow containing particles for even n is passed to the first ("A") mass detector and the airflow containing particles for odd n is the second ("B"). ) Flows through the mass detector, Δm _A / Δt represents the mass ratio measured by the first mass detector, Δm _B / Δt represents the mass ratio measured by the second mass detector, and Δm / Δt is the correction represents mass ratio, [Delta] V _n is the measurement period n
Represents the volume of gas sampled during F, F represents the flow rate, and MC represents the corrected mass concentration. In the above equation (4), the indexing to (-1) is for performing the subtraction of the measured value.

FIG. 3 shows another embodiment of the particle mass difference measuring apparatus of the present invention. In the measurement device 40, the gas 42 containing particles is drawn into the particle diameter selective inlet 44 having a normal structure, and then branched into three gas flows 46A, 46B, and 46C. The air streams 46A and 46B containing the particles are supplied to an optional dryer or dehumidifier 47 (eg, Perma).
Nafion's Perma Pure PD ^™ series gas dryer commercially available from Pure Inc, Toms River, New Jersey), then flow through each of the selectively operable particle removers (eg, electrostatic precipitators) 48A, 48B, and then mass. Detector (for example, tapered element vibration micro balance) 50
Flow through each of A and 50B. Airflow 46A and 46B using dryer 47
It is advantageous to reduce, control, or eliminate the water vapor in. The airflow 46C is a bypass flow, and the flow rate passing through the inlet 44 can be adjusted. The flow controllers 52A, 52B, and 52C serve to maintain each of the air flows 46A, 46B, and 46C at a desired constant flow rate, and to equalize the flow rates at the respective mass detectors 50A, 50B. For example, when the outflow rate of the inlet 44 is 16.7 liter / minute, the flow controllers 52A and 52B can maintain the flow rate of each of the air flows 46A and 46B at 2.0 liter / minute, and the flow controller 52C , The flow rate of the airflow 46C can be maintained at 12.7 liters / minute. The desired flow rate is obtained by a common vacuum pump working in conjunction with the flow controller.
The particle remover switch 56 is turned on by a command from the controller 58.
, 48B are alternately activated during successive measurement periods. Controller 5 easily controlled by microcomputer or other known processor
8 also controls the frequency counter data analyzer 60, and outputs the mass detectors 50A, 5A.
The frequency measurement is received from OB and converted to a mass measurement in a known manner. From these mass measurements, at least one of the mass and concentration of the particulate matter in the gas stream 42 containing the particles is quantified as described above and sent to the output device 62.
As those skilled in the art can easily understand, the controller 58, the data analyzer 60
, Output device 62, and other components of the device can take a variety of different forms.

The operation of the device 40 is the same as described above for the device 10. Device 40
Thus, the configuration can be simplified in that a single inlet and a control system can be used to obtain corrected mass concentration data.

FIG. 4 shows actual test results with a particle mass difference monitor of the present invention and a single tapered element vibrating microbalance operated at the same location during the same time period. Plot 64 represents the concentration at ambient temperature measured by the mass difference monitor, and plot 6
6 represents concentration measurements obtained from a single tapered element vibrating microbalance kept at 50 ° C. As expected, the calorimetric monitors of the present invention that internally correct for volatilization losses show higher concentration levels.

Although preferred dual detector embodiments have been described and described herein, it will be obvious to those skilled in the art that various changes, substitutions, additions, and the like can be made without departing from the spirit of the invention. That is. For example, to generate an airflow that does not contain the desired particles,
Instead of using one particle remover, one particle remover can be used. First
And in the second mass detector, switching between the particle-free air flow and the particle-containing air flow can be achieved by mechanically switching one particle remover between gas flow paths or by using two mass detectors. This can be done by mechanically switching the outlet of one particle remover between them, for example with a valve, or mechanically switching the position of the two detectors.
Instead of an electrostatic precipitator, a filter such as a low pressure drop electrolet filter or other particle remover can be used. Depending on the intended application and operating conditions, a denuder that reduces gaseous components, a temperature and / or humidity controller (as taught in PCT / US99 / 00687), and at least other gas and particulate matter. One conditioning device can also be used with the particle mass difference monitor. The measurements obtained with the two mass detectors are:
Includes frequency, mass, mass ratio, mass concentration, and other parameters.

In a single detector embodiment of the present invention, a gas flow containing particles and a gas flow substantially identical thereto but without particles are alternately passed through the mass detector during successive measurement periods. Swept away. To take the difference between successive measurements obtained with a mass detector in a suitable short measurement time and add the mass lost due to volatilization during the measurement period to the measured gain of the collected particulate matter Gives an accurate measurement of the total mass of the particles in the airflow.

One embodiment of the single detector of the particle mass measurement device of the present invention is illustrated in FIG. Apparatus 10 'includes an inlet 12 in air communication with a selectively activated particle remover 14 and a mass detector 16 . The air flow 18 containing the particles is
And passes through a selectively activated particle remover 14 and continuously mates with a mass detector 16.

The inlet 12 typically includes a separator for pre-separating particles larger than a predetermined cutoff size from the gas stream containing the particles. For example, an inlet lobe having a PM10 and / or PM2.5 separator is known and commercially available.

The inlet 12 into which the air stream containing the particles flows enters the particle remover 1 which can be selectively operated next.
Connect to 4 and go through it. The activated particle remover 14 removes substantially all particles from the air stream with little effect on the temperature, pressure and / or flow rate of the air stream. It is advantageous to perform such particle removal using the same type of electrostatic precipitator that is commonly used in commercially available air purifiers. To reduce the production of ozone, a positive corona and an electrostatic precipitator operating at very low current, for example of the order of tens of nanoamps, are preferred. The current must be sufficient to cause the depositor to remove substantially all particulate matter.

The particle remover 14 is selectively activated during a subsequent alternating measurement period to remove particulate matter from the gas stream 18 during a subsequent alternating measurement period.

For example, during the first measurement period, the particle remover is turned on, and during the next measurement period, the particle remover 14 is turned off. This alternating operation pattern continues during successive measurement periods. Advantageously, each measurement period is relatively short, preferably about 15 minutes or less, more preferably about 5 minutes or less, and most preferably about 1 minute or less.

The airflow 18 generated from the particle remover 14 continuously intersects with the mass measuring device 16 throughout the continuous measurement period.

While other direct or indirect mass detectors such as quartz crystal microbalances, β-ray absorption monitors, pressure drop monitors, etc. may be used, the mass detector 16 which is considered preferred is a tapered hollow element vibrating microbalance. The latter device is preferable because it has high sensitivity to mass, can perform real-time measurement, is mass measurement based on direct inertia, and filters using high collection efficiency.

Since the mass to be measured is on the order of micrograms and sub-micrograms, high mass sensitivity is important. Real-time measurement is important because mass volatilization occurs in a short time frame. Direct mass measurement is desirable to avoid ambiguity in the measured value, while at the same time tracking and correcting the mass standard. Filtration guarantees high collection efficiency. A suitable tapered element vibrating microbalance is disclosed in commonly owned U.S. Pat. No. 4,391,3.
No. 38, and more information is provided in US Pat. No. 3,926,271. The findings of these two patents are incorporated herein by reference.

In a preferred microbalance, the tapered hollow element oscillates in a clamp-free mode. A filter is attached to the free end of the device and serves to trap particulate matter from the gas stream containing the particles. When this airflow passes through the filter and then through the hollow element, the vibration frequency of the hollow element changes with the mass load of the filter and can easily be converted to a mass measurement. For the purposes of the present invention, the change in the vibration frequency of the vibrating element for each measurement period is converted into a mass ratio (i.e., the change in mass over the measurement time interval), resulting in a corrected mass concentration as described in more detail below. .

A tapered hollow element vibrating microbalance is preferred, but in other forms or shapes, such as operating in other modes such as non-tapered, tuning fork or U-shaped, or clamp-free mode, or A collector that typically vibrates perpendicular to the plane of the collector, or a collision plate or other particle collector, may also be used as the mass detector.

In operation, the particle remover 14 is turned off, and the mass detector 16 changes in mass and the shadow of the instrument.
Effective mass M due to frequency change derived from Hibiki_AeffIs measured over time Δt.
M_Aeff= M_P+ M_P ^v+ ΑM_G+ Β + γΔP (1) where M_P= Non-volatile component of particle mass M_P ^v= Volatile component of particle mass αM_G= Acquisition / desorption of filter and gas acquisition by evaporation of deposited material
Or loss mass βΔt = effective mass equivalent of frequency change due to temperature change Δt during time Δt γΔP = effective mass equivalent of frequency change due to pressure change ΔP during time ΔP (βΔ
t and γΔP represent the main device artifacts) During the subsequent time Δt, the particle remover 14 is on and M_PAnd M_P ^vIs removed
It is not detected by the mass detector 16. Also M_Beff= ΒΔt + γΔP (2) Therefore, M_Aeff-M_beff= M_P+ M_P ^v+ ΑM_G+ ΒΔt + γΔP- (αM _G + ΒΔt + γΔP) = M_P+ M_P ^v (3) These measurement periods Δt are used for the rate of change of the particle concentration and for the measurement of mass such as temperature and pressure.
It is kept relatively short compared to the influencing factors, so the effects of volatilization,
Gas / vapor adsorption / desorption effect and the effect of pressure change are measured twice
It remains the same during the period, allowing accurate subtraction.

When the particle remover 14 does not operate during a particular measurement period, the mass detector 16 provides a measurement of the mass that is representative of the mass of the particulate matter collected during that period, ie, the acquired mass. I will provide a. The effective value of the mass lost due to volatilization during that same period is provided by the mass detector during successive measurement periods during which the mass detector 16 intersects the particle-free (particle remover activated) airflow. Is done. The two mass measurements are subtracted and the loss mass is effectively added to the measured gain mass to obtain a corrected and accurate value of the mass of the particulate matter.

In practice, measurements can be made based on mass ratio, using the switching time as a convenient time reference. By subtracting the mass ratio, small correction errors in the measurement system will only result in comparable final errors in the results. If the mass is used directly, this error can accumulate to unacceptable levels as the monitoring time continues.

FIG. 6 shows an example of how the mass changes during the subsequent four measurement periods, as measured by the detector 16 of the device of FIG. The corrected mass concentration can be calculated according to the following relation:

[0065] ^{(-1) n + 1 (Δm} B / Δt) n + (- 1) n (Δm A / Δt) n = (Δ
m / Δt) _n (4) and (MC) _n = (Δm / Δt) _n (1 / F) = Δm / ΔV _n (5) where Δt represents the time interval during the measurement period, and n is the measurement time An airflow containing particles for even n crosses the first (A) mass detector, an airflow containing particles for odd n crosses the second (B) mass detector, Δm _A / Δt represents the mass ratio measured by the first mass detector, Δm _B / Δt represents the mass ratio measured by the second mass detector, Δm / Δt represents the corrected mass ratio, and ΔV _n represents the measured mass ratio. Represents the volume of gas sampled during period n, F represents the flow rate, and MC represents the corrected mass concentration.

In the above equation (4), the measurement value is subtracted by indexing (−1).

FIG. 7 shows another embodiment of the single detector particle mass difference measuring apparatus of the present invention. An air stream 42 containing particles passes through a particle size selection inlet 44 of conventional construction and a measuring device 40 '.
And then split into two air streams 46A and 46C. The air stream 46A containing the particles may be an optional dryer or dehumidifier 47 (eg, Perma
Nafion's Perma Pure PD ^TM Series Gas Dryer, commercially available from Pure Inc, Toms River, New Jersey)
Then, it flows through a particle remover (eg, an electrostatic precipitator) 48 that can be selectively activated, and then intersects with a mass detector (eg, a tapered element vibrating microbalance).
It is advantageous to use a dryer 47 to reduce, control or remove water vapor in the airflow 46A. The air flow 46C is a bypass flow, and the flow rate passing through the inlet 44 can be adjusted. The flow controllers 52A and 52C serve to maintain a desired constant flow rate in the airflow 46A and in the mass detector 50. For example, when the outflow speed of the inlet 44 is 16.7 liters / minute, the flow controller 52A can maintain the flow rate of the air flow 46A at 2.0 liters / minute, and the flow controller 52C adjusts the flow rate of the air flow 46C to 14 liters / minute. 0.7 liters / minute. The desired flow rate is obtained by a common vacuum pump operating in conjunction with the flow controller. The particle remover switch 56 activates the particle remover 48 during a measurement period following the command taking of the controller 58. A controller 58, which is easily controlled by a microcomputer or other known processor, also controls the frequency counter data analyzer 60, receives the frequency measurement from the mass detector 50, and converts this frequency measurement into a mass measurement in a known manner. Convert. From these mass measurements, the mass and / or concentration of the particulate matter in the gas stream 42 containing the particles is quantified by the analyzer 60 as described above and sent to the output device 62. As those skilled in the art will readily appreciate, switch 56, controller 58, data analyzer 60, output device 62, and other components of the device may be of a variety of different types.

The operation of device 40 ′ is the same as described above for device 10 ′.

Although a preferred single detector embodiment has been described and described herein, it will be obvious to those skilled in the art that various changes, substitutions, additions, etc. can be made without departing from the spirit of the invention. I think that the. For example, switching between a particle-free air flow and a particle-containing air flow for a mass detector may be a mechanical switch between a particle-containing air flow and a particle-free air flow, such as a mechanical switch in the position of a valve or detector, and the like. A variety of alternative approaches can be used. Rather than an electrostatic precipitator, it is also possible to use a filter, for example a low pressure drop electrolet filter or other particle remover. Depending on the intended application and operating conditions, a denuder, temperature and / or humidity controller to reduce gaseous components (PCT / US99 / 006 sharing patents)
87, and other airflow and / or particulate conditioning devices can also be used with the particle mass difference monitor. The measurements provided by the mass detector include frequency, mass, mass ratio, mass concentration and other parameters.

[Brief description of the drawings]

FIG. 1 shows a simple schematic diagram of one embodiment of a dual detector particle mass difference measuring apparatus of the present invention.

FIG. 2 shows that the corrected mass concentration is 2% of the particle mass difference measuring device of the present invention.
5 is a graphical representation useful in understanding how it is derived from the mass ratio measurement of a double detector.

FIG. 3 shows another embodiment of the dual detector device of the present invention.

FIG. 4 is a graph showing a comparison between an actual measurement of the concentration of particulate matter obtained by the particle mass difference measuring apparatus of the present invention and a measurement obtained by a single-taper element vibration microbalance.

FIG. 5 is a simplified schematic diagram of one embodiment of a single detector particle mass difference measuring apparatus of the present invention.

FIG. 6 is a graphical representation useful in understanding how the corrected mass concentration is derived from a single detector mass ratio measurement of the particle mass difference measurement device of the present invention.

FIG. 7 shows another embodiment of the single detector device of the present invention.

[Explanation of symbols]

 12 Insulation Block 15 Plural Layers of Flexible Insulating Foam 26 Pressure Cover

──────────────────────────────────────────────────の Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), AU, CN, JP (72) Inventor Raplet, Jorg United States, 12186 New York, Boorheathville, Crow Ridge Road 33

Claims (31)

[Claims] An apparatus for measuring particulate matter in an air flow containing particles (46A) (1)
40 ') comprising: a mass detector (50); and a first means (48) for providing a particle-free airflow substantially identical to said airflow containing particles except for particles. An apparatus (40 ') comprising switching means (56) for alternately intermingling said mass flow (50) with said mass flow containing particles during said continuous measurement period. ). 2. The method according to claim 1, wherein the first measurement time is provided for a current measurement time provided by the mass detector.
Second means (60) for measuring a difference between the measured value and a second measured value for a subsequent measuring time provided by the mass detector (50), the difference being used during the current measuring time. The apparatus (40 ′) according to claim 1, wherein the volatilization loss caused in the gas is corrected internally, and the mass or concentration of the particulate matter in the gas stream containing the particles is determined from the difference. 3. The mass detector comprises a first mass detector (50A) and a second mass detector.
A first mass detector (50A) and a second mass detector (50B) having a mass detector (50B), and the switching means (56) converting the airflow containing particles and the airflow not containing particles to the first mass detector (50A); Each of them is alternately mated during the subsequent measurement time, and the first measurement value provided by the first mass detector (50A) and the first mass detector (50B) provided for each of the subsequent measurement times. A second means (60) for measuring the difference between the second measurements, wherein said difference internally corrects for volatile losses occurring during said measurement time, and from said difference a gaseous stream containing particles. Device (40) according to claim 1, characterized in that the mass or concentration of the particulate matter is determined. 4. The first means (48) comprises particle removal means for removing substantially all of the particulate matter from the gas stream containing particles and providing the gas stream free of particles. Device according to any one of the preceding claims, wherein
40, 40 '). 5. The method according to claim 4, wherein said particle removing means removes said particulate matter from said air stream containing particles while keeping the temperature, pressure and flow rate of said air stream substantially the same. Item (40, 40 '). 6. The device (40, 40 ′) according to claim 5, wherein said particle removing means is an electric dust collector. 7. Apparatus (40, 40 ′) according to claim 6, characterized in that the particle removal means operates in a low current, positive corona mode. 8. The first means (48) includes a pair of electric dust collectors (48A, 48B).
The switching means (56) further comprises means for alternately controlling and operating only one of the pair of electric precipitators during the subsequent measurement time. Item (40). 9. Device (40, 40 ′) according to any one of the preceding claims, characterized in that each mass detector (50) has a vibrating element microbalance.
. 10. Apparatus (40) according to any one of the preceding claims, characterized in that it comprises a dryer (47) for reducing water vapor in the particle-containing and particle-free gas streams. , 40 '). 11. Apparatus according to claim 1, characterized in that the measurement value provided by each mass detector (50) is a mass ratio measurement value.
40 '). 12. The apparatus according to claim 1, further comprising a flow control means for maintaining substantially the same air flow in each of the detectors during the measurement period. Device (40) according to clause 3. 13. The switching means (56) comprises: (a) during an even-numbered period subsequent to the measurement time, the air flow containing particles, respectively, is mixed with the first mass detector (50A) to contain particles. (B) combining the air flow containing particles with the first mass detector (50B) during each of the subsequent odd-numbered periods of the measurement time; An apparatus (40) for simultaneously intermingling the particle-free airflow with the second mass detector (50A), wherein the first measurement value and the second measurement value are in even-numbered periods of the measurement time Respectively, wherein the first measured value and the second measured value respectively represent the lost mass and the acquired mass during an odd-numbered period of the measurement time, and the second means (60) Then Effectively adds to acquire mass loss mass during the measurement period, according to claim 3 claims, characterized in that quantifying the mass or concentration of particulate matter in the air flow containing the particles (40). 14. Switching means (56) for: (a) detecting an air flow containing particles during an even period of a subsequent measurement time by a mass detector (50);
(B) a device (40 ') for mating a particle-free airflow with a mass detector (50) during an odd numbered period of the subsequent measurement time, wherein the detector (50) contains particles. If the airflow is combined, the detector measures the acquired mass, and if the detector (50) is combined with a particle-free airflow, the detector measures the lost mass, and the second means (60) measures the acquired mass. Effectively adding the mass to the measured loss mass,
Device (40) according to claim 2, characterized in that the mass or concentration of particulate matter in an air stream containing particles is determined. 15. Apparatus (40, 40 ′) according to claim 13 or claim 14, characterized in that the lost mass represents a volatile component of the particulate matter. 16. Apparatus (40, 40 ′) according to claim 15, wherein each of said subsequent measuring periods lasts for about 15 minutes or less. 17. Apparatus (40, 40 ′) according to claim 15, wherein each of said subsequent measuring periods lasts within about one minute. 18. The quantitative value of particulate matter in an airflow containing particles is calculated by the following relational expression:
Claim 3 characterized in that it has a corrected mass concentration calculated by
The described device (40): (-1)^{n + 1}(Δm_B/ Δt)_n+ (− 1) n (Δm_A/ Δt)_n= (Δm
/ Δt)_n, And (MC) n = (Δm / Δt)_n(1 / F) = Δm / ΔV_n  Here, Δt represents a time interval of the measurement period, n represents a measurement period index, and for an odd number n, the air flow containing particles is mixed with the first mass detector (50A).
For even n, the air stream containing particles is combined with the first mass detector (50B).
, Δm_A/ Δt represents the mass ratio measured by the first mass detector (50A), and Δm_B / Δt represents the mass ratio measured by the second mass detector (50B), Δm / Δt represents the corrected mass ratio, ΔV_nRepresents the volume of the gas sample during the measurement period n, F represents the flow rate, and MC represents the corrected mass concentration. 19. The quantitative value of particulate matter in an airflow containing particles is calculated by the following relational expression:
3. The method according to claim 2, wherein the corrected mass concentration is calculated by
The described device (40 '): (-1)^{n + 1}(Δm_B/ Δt)_n+ (− 1) n (Δm_A/ Δt)_n= (Δm
/ Δt)_n, And (MC) n = (Δm / Δt)_n(1 / F) = Δm / ΔV_n  Where Δt represents the time interval of the measurement period, n represents the measurement period index, and the odd-numbered n intersects the air flow containing particles with the mass detector (50), and the even-numbered n Is mixed with the mass detector (50), and Δm_A/ Δt represents the mass ratio measured by the mass detector (50), and Δm_B/ Δt
Represents the mass ratio measured by the mass detector (50), Δm / Δt represents the corrected mass ratio, ΔV_nRepresents the volume of the gas sample during the measurement period n, F represents the flow rate, and MC represents the corrected mass concentration. 20. An air flow containing particles is mixed with a first detector (50A), and an air flow containing no particles is mixed with a second detector (50B).
A particle mass difference measurement system (40) used as a standard to offset the effect of the detector instrument from the measurements provided by the mass detector, wherein the particle-containing airflow and the particle-free airflow are continuous. The first mass detector (50A) and the second mass detector (50B) alternately intersect each other during the measurement period, thereby causing a volatile loss occurring during the subsequent measurement period. Wherein the correction is made internally. 21. A device (40 ') for measuring particulate matter containing volatile components in an air flow containing particles, wherein the mass detector (50) and the mass detector (50) are constantly intermingled with each other. Means for directing said airflow, said means for removing particles being located upstream of said mass detector, wherein substantially all of the particulate matter is activated when said means for removing particles is actuated. A measuring device (40 '), characterized in that control means (58) activates said particle removing means (48) during said subsequent alternating measuring periods after being removed from said airflow. 22. An apparatus (40) for measuring particulate matter containing volatile components in an air stream containing particles, wherein the air stream containing particles is divided into a first air stream (46A) and a second air stream (46B). A first mass detector (50A) and a first mass detector (50B); a means for directing an airflow to constantly intersect the first airflow (46A) with the first mass detector (50A); Means for directing the air flow so as to constantly mix the air flow (46B) with the second mass detector (50B); first air flow particle removing means (48) disposed upstream of the first mass detector (50A).
A) wherein, when the first particle removing means is operated, the first airflow particle removing means (48A) for removing substantially all the particulate matter from the first airflow (46A); Second airflow particle removing means (48) located upstream of the mass detector (50B)
B), when the second particle removing means is operated, a second airflow particle removing means (48B) for removing substantially all particulate matter from the second airflow (46B); The airflow particle removing means (48A) and the second airflow particle removing means (48B)
Control means (58) for activating only one of them alternately during successive measurement periods
Means for measuring a difference between a first measurement value provided by the first mass detector (58A) and a second measurement value provided by the second mass detector (58B) during each subsequent measurement time. (60) wherein the difference is provided with means (60) for internally correcting the volatilization loss occurring during the measurement period and quantifying the mass or concentration of the particulate matter in the gas stream containing the particles from the difference. An apparatus (40) characterized by the above. 23. Apparatus (40, 40 ') according to claim 21 or 22, characterized in that said particle removal means (48) is an electric precipitator. 24. An apparatus (4) for measuring the mass of particulate matter in an air stream containing particles.
0), wherein the first mass detector (50A) and the second mass detector (50B) have a particle-free airflow source substantially identical to the particle-containing airflow except for the particles. Switching means (56) for alternately intersecting the airflow containing the particles and the airflow not containing the particles with the first detector (50A) and the second detector (50B) alternately during a continuous measurement period, And a data analyzer (60) for obtaining a difference between the first mass detector (50A) and the second mass detector (50B) during the subsequent measurement period, and the difference is used for the measurement period. An apparatus (40) having an analyzer for internally correcting a volatilization loss occurring therein and quantifying the mass or concentration of the particulate matter in an air stream containing particles from the difference. 25. Combining an air flow containing particles with a first mass detector (50A);
A first mass detector collects a current particle sample from the airflow during the current measurement period and measures the resulting mass, and a second mass detector (50B) counteracts the influence of the detector instrument. Mass difference measurement method used as a standard for measuring a change in the properties of particles occurring during the current measurement period, using a second mass detector (50B) for measurement. Measurement method. 26. The method according to claim 25, wherein said change in particle properties is a mass loss due to volatilization of the collected volatile particles. 27. The mass lost due to volatilization measured by the second mass detector (50B) is added to the gained mass measured by the first mass detector (50A), and the mass obtained during the current measurement period is calculated. 27. The method according to claim 26, wherein the corrected particle mass is measured. 28. The measured lost mass occurs in a particle sample collected earlier during the current measurement period, and the initially collected particle sample is formed in the second mass detector during an earlier measurement period. 28. The method of claim 27, wherein the method was collected at (50B). 29. The current measurement period and the previous measurement period are sufficiently short, and the volatilization of the initially collected sample and the currently collected particle sample during the current measurement period is substantially the same. 29. The method according to claim 28, wherein the method is able to ensure that: 30. Particles in which an air stream containing particles is intermingled with a mass detector (50), during which a mass detector collects a current particle sample from said air stream during the current measurement period and thereby measures the mass gained. In the mass measurement method, the mass lost by volatilization of the collected volatile particles during the current measurement period is measured, and the measured mass loss is added to the measurement gain mass, and the mass loss is corrected during the current measurement period. An improved method for measuring particle mass. 31. A mass detector wherein the lost mass is the same during a subsequent period.
31. A method according to claim 30, characterized in that it is measured with a second mass detector (50B) during the current measurement period.